This page will detail just a few of the infinite number of alternate timelines in the universe. Many of these are taken from the LUG ST:RPG supplement- All our Yesterdays. Ships from each detailed universe and others are original and will be placed here as well.
 
 

In the normal timeline, the Borg Invaded Federation space in 2366 with a single cube ship. The Borg cube devastated a Federation fleet at Wolf 359 and made its way to Earth orbit before being stopped by the actions of the crew of the USS Enterprise-D. The Borg ship self-destructed as a result.
In this timeline, the efforts of the Enterprise crew were unsuccessful in stopping the Borg, who conquered Earth and assimilated its population and technology. So began a systematic Borg assault on the civilizations of the Alpha Quadrant. Borg drones on Earth began the immediate construction of new ships, which spread out towards other Federation worlds, attacking and assimilating them in turn. Federation ships and weapons proved useless against the Borg's superior technology. Although Starfleet personnel were able to win some minor victories, they could not halt the Borg's advance. With each planet they assimilated, the Borg grew stronger while the Federation weakened.
In an unprecedented move, the major powers of the Alpha and Beta Quadrants-the Federation, the Romulan Empire, the Klingon Empire, and the Cardassian Union-formed an alliance to fight against the Borg. Even with their combined fleets and firepower, the new alliance could not overcome the Collective. They slowly continued to fall back against the Borg onslaught, which quickly overran most of Federation and Klingon territory, as well as large portions of Cardassian and Romulan space. By 2370, the Borg controlled the majority of alliance territory and continued to expand. They assimilated the Bajor Sector before the discovery of the Bajoran wormhole, so it remains unknown, although some alliance survivors find hope in Bajoran legends of a "celestial temple." A few desperate explorers hope to find the temple as a refuge or a source of allies against the Borg. The Borg onslaught also encouraged the Romulans to reveal the existance of the Taurhaui Unity to the rest of the alliance, which is hoping to petition the Taurhaui for aid.
(From All our Yesterdays sourcebook for ST:TNG RPG by Last Unicorn Games)
USS Enterprise-D
USS Excalibur
Avenger Class Destroyer
Plasma Bird of Prey
Borg Attack Sphere
 

Recommendations for other ship SSDs available: Federation - No ships above 3Xl except for above. Ph-9s and Quan are rare. Galaxy Class represents the most advanced ships in the remaining fleet.
Romulan, Klingons, Cardassians - No change, advancement proceeds at the same rate.
No Dominion, Breen, or Ferengi
Other races - use best judgement
 
 

In 1270, early in its space flight era, Vulcan was attacked by a fleet of unknown vessels emerging from a wormhole in its star system. For a century, the Vulcans repelled attacks from this fleet, eventually driving them from their system altogether. The Vulcans did not learn until much later that the attacking fleet was made up of Romulans, a faction of exiled Vulcans.
In this timeline, the first Romulan-Vulcan war resulted in victory for the Romulans, who retook their homeworld and instituted a new military controlled government there. When the wormhole connecting the Vulcan and Romulan star systems closed, the Romulans already held Vulcan in a tight grip. The Vulcans opposed the Romulans through passive resistance, which failed to move the conquerors. The teachings of Surak were outlawed, and its followers were forced underground. Over time, Vulcan culture became more and more Romulan in character, reverting back to its warrior roots, but mote unified than before.
Cut off from contact with Romulus because of the lack of warp technology and subspace radio, Vulcan continued on its own for centuries. When they developed warp drive, the Vulcans (who no longer called themselves Romulans) began to expand out into space. They conquered several nearby star systems and sent envoys to make contact with their cousins on Romulus. At first, the future of the Vulcan race looked bright, but trouble quickly developed.
Both Vulcan and Romulus considered themselves the center of a new empire, based on the Way of D'era. The Romulans believed they were the true inheritors of the Way, since it was their ancestors who first left Vulcan. The Vulcans believed they, as the homeworld, deserved that position. Political tensions quickly gave way to war between the two powers.
In the meanwhile, a Vulcan scout vessel encountered a warp signature in the Sol system and made first contact with Earth. Vulcan warriors easily conquered the war-torn Earth, followed not long thereafter by Alpha Centauri, itself recovering from a deadly plague. The Vulcans formed an alliance with the warlike Andorians, bringing them into the Empire as allies against the Romulans. The Romulans, in turn, have made overtures to the Klingon Empire and established a shaky alliance with them. Vulcan military commanders like Sarek won brilliant victories over the Romulan Empire before the Romulans developed cloaking technology. This led the two powers to declare a truce and create the Vulcan Neutral Zone, warily watching each other as they rebuild their fleets.
(From All our Yesterdays sourcebook for ST:TNG RPG by Last Unicorn Games)

Vulcan War Cruiser
Vulcan R'derix Destroyer
Romulan K'vort Light Cruiser
Romulan K'tinga Light Cruiser
 
 

In 2370, Worf unknowingly ruptured a quantum fissure, breaking down the walls between parallel dimensions and causing some 285,000 alternate realities to merge (possibly more, but any without an Enterprise would not have been noticed) In this alternate reality, the rupture was stabilized, but all of the ships and crews remained. Plans were quickly developed to use adapted transporters to beam crew members back to there own parallel universe using their quantum signature and a positive safe location they were aware of in their universe (in most cases, Earth) This left almost 200,000 crew members who could not or would not be sent back. It also left 285,000+ Galaxy Class Vessels floating in space. Of the 285,000 vessels, 250,000 were in optimum operational condition. Of the 250,000, 50,000 are being scrapped for parts, replicators, power cores, etc. to be spread throughout the Federation, 300+ were assigned permanent guard duty among the Federation Worlds and Colonies (about 2 per planet), and 10,000 plus were refitted and replaced almost every other ship class the Federation had. Galaxy class vessels are used for Exploration, Science Missions, Transports, even Luxury liners and Amusement centers. After every possible option for using a Galaxy class vessel had been exhausted, they were left with over 100,000 ships. They currently reside in 5 seperate, uninhabited systems, floating in huge groups in open space. Some have been stolen and destroyed, but many just sit silently and unused.
The Federation in this parallel universe is the powerhouse of the Galaxy. The single Borg Cube invasion of 2373 was met with almost 200 Galaxy Class vessels and destroyed quickly. The Romulans have hidden behind their own borders, the Cardassian DMZ was never created due to the fear of Federation military might. The only potential enemy to the Federation in this universe would be the Dominion, who they have not encountered yet.
The Federation is a virtual paradise, even compared with the 'normal' universe. Only Orion raiders and other pirates raid the Galaxy stockyards for the occasional parts or even ship. The Federation has other problems building though...The Romulans, Cardassians, and Breen have forged a secret alliance out of fear of the Federation. They have made contact with a powerful group in the Gamma Quadrant as well as several smaller empires in plans to destroy the Galaxy stockyards and reduce the Federation down to tolerable levels. Their plans are to use cloaking technology to plan a huge multi-level assault on the Federation shipyards. They have already outfitted hundreds of Cardassian and Breen vessels with cloaks and are sharing the technology with the Dominion to tempt them into the alliance.
Meanwhile, the Borg have not forgotten about Earth....
Galaxy Class Fire Control Cruiser
Galaxy Class Cargo Ship